1. Field of the Invention
The present invention relates to a method of and an apparatus for determining exposure amount in a copying apparatus, and more particularly to a method of and an apparatus for determining exposure amount in a copying apparatus for reproducing an image recorded on a film onto a reproducing material such as a printing paper.
2. Description of the Related Art
In general, when a color image is copied onto a copying material such as a light-sensitive material from a color original picture, exposure amount is determined with respect to the respective colors of red (R), green (G), and blue (B) light by measuring integral transmission densities of the R, G, and B light by using a photometric device having color separation filters comprised of dye filters or evaporated filters. In order to determine the exposure amount accurately, it is necessary for the spectral sensitivity distribution of the photometric device to accurately coincide with the spectral sensitivity distribution of the copying material. The spectral sensitivity distribution of this copying material is a complicated distribution which exhibits asymmetry with respect to a wavelength at which sensitivity becomes maximum. For this reason, in preparing the color separation filters by means of the dye filters and evaporated filters, it is necessary to combine a multiplicity of filters, so that there are problems in that it is difficult to mass produce them and their accuracy is low.
Accordingly, in a photoresist exposure apparatus, a technique is known wherein the spectral sensitivity distribution of a photometric device is made to coincide with the spectral sensitivity distribution of a copying material by separating the light from an original picture into spectral components and by effecting processing by adding weight to the separated components. Japanese Patent Application Laid-Open No. 88624/1983 discloses a technique in which the aforementioned processing is effected by using a photoresist exposure apparatus comprising a diffraction grating, a convergent optical system, and a photodetector. However, a complicated mechanism is required to ensure that the spectral sensitivity characteristics will not change owing to the relative arrangement of these optical elements. Japanese Patent Application Laid-Open No. 95525/1986 discloses a photoresist exposure apparatus in which a multiplicity of interference filters are arranged instead of the aforementioned diffraction grating. However, since the interference filters of the same number as that of the separated components of light are required, if the number of photometric wavelengths is numerous, mass production is difficult.
In addition, in a color photographic printer, Japanese Patent Application Laid-Open No. 134353/1989 discloses a technique in which light transmitted through an image recorded on a film is separated into spectral components by means of a prism, a diffraction grating, or spectral filters, and an image of a part of a copy original is formed on a panel of photoelectric sensors into the configuration of a slit. In this technique, the light at different photometric positions is made incident along a row of the panel of the photoelectric sensors, and spectral light for each photometric position made incident along columns of the panel is converted to electrical signals. At the same time, by gradually moving the film, the portion of an original image through which the slit light is transmitted is moved, so as to photometrically measure the entire image plane. Each spectral component of each photometrically measured pixel is multiplied by a weighting coefficient corresponding to a spectral sensitivity distribution of the copying material, so as to determine photometric values which are equivalent to those obtained by conducting photometry by means of the sensors having a spectral sensitivity distribution equivalent to that of the copying material.
However, if the diffraction grating or the spectral filters are employed, the same problem as the one described above is encountered. If the prism is used, since the light is separated by refraction, there are drawbacks in that it is necessary to make the projected light into parallel light, that the apparatus becomes large in size, and that it is difficult to photometrically measure the spectra with the same quantity of light by using the same panel because of the spectral sensitivity distribution of the photoelectric sensors. In addition, there is a drawback in that since the rows are decomposed into the columns, there occurs a substantial decline in the quantity of light particularly when the density of the image is high. For this reason, photometry is conducted by decreasing the spectral resolution, and an interpolation is provided for the photometrically measured spectra.
Furthermore, Japanese Patent Application Laid-Open No. 142719/1989 discloses an apparatus comprising: a first photometrically measuring section for effecting photometry by using a two-dimensional array sensor by separating slit light projected onto an image recorded on a film into a multiplicity of spectra by means of a prism, a diffraction grating, and the like so as to determine an average density; and a second photometrically measuring section for determining an average density by means of scanning photometry so as to determine an exposure amount, wherein the exposure amount is corrected on the basis of results of comparison between the average density determined by the first photometrically measuring section and the average density determined by the second photometrically measuring section. However, since the prism and the diffraction grating are used, a problem similar to the above-described problem is encountered. In addition, since two photometrically measuring sections need to be provided, there has been drawbacks in that the apparatus becomes large in size, and that the restrictions imposed on the layout of the component parts become large.
To overcome these problems, the present applicant has proposed an exposure-amount controlling apparatus (Japanese Patent Application Laid-Open No. 230148/1991) comprising: a first sensor for separating a film image into a multiplicity of spectra and photometrically measuring them; and a second sensor having maximum sensitivities at wavelength bands corresponding to three sensitivity wavelength bands of a copying material for effecting photometry by dividing an image into a multiplicity of segments, wherein an average density PD1j is determined by multiplying a photometric value of the first sensor by a weighting coefficient corresponding to a spectral sensitivity distribution of the copying material, a tricolor average density PD2j and a correction amount PD3j are determined by the second sensor, and an exposure amount is determined on the basis of the two variables. In this technique, the exposure control amount for determining the exposure amount PDj is determined from EQU PDj=PD1j+F.multidot.f(PD2j+PD3j)
In the above-described exposure-amount controlling apparatus, it is possible to effect photometry by using diffused light since the first sensor is constituted by a two-dimensional image sensor and an interference filter in which the thickness of an interference film is varied continuously or in steps in such a manner that the wavelength of the color to be separated, i.e., the wavelength to be spectrally diffracted, changes. However, since it is necessary to provide two photometrically measuring sections, it is difficult to make the apparatus compact. In addition, unless the light transmitted through the film image and made incident upon the first sensor is diffused and rendered uniform, a spectral error occurs, so that a proper exposure amount cannot be obtained.
In addition, in the above-described technique, in a case where the spectral sensitivity distribution of the second sensor, in particular, is substantially different from the spectral sensitivity distribution of the copying material, and differs substantially from the spectral sensitivity distribution of the first sensor, e.g., in a case where the spectral sensitivity distribution is relatively sharp (the half-width is small), it is necessary to change the coefficient F in the formula of the exposure control amount PDj by a large degree in correspondence with the film type and the exposure level. Hence, it has been difficult to obtain a proper exposure amount.
In a method of determining exposure amount in an image copying apparatus (Japanese Patent Application Laid-Open No. 46648/1991), tricolor photometric data is set as tricolor normalized data by being transformed in accordance with a normalization condition, a comparison is made between the tricolor normalized data and a reference value to classify the tricolor normalized data, and the exposure amount is determined on the basis of an average density of the tricolor photometric data selected in accordance with that classification. As a result, a proper exposure amount is obtained irrespective of the type of film on which the image is recorded, but no consideration is given to the matching of the spectral sensitivity distribution of the photometrically measuring means with the spectral sensitivity distribution of the copying material.
Meanwhile, a method has been conceived in which the energy distribution of a light source used for photometry, the spectral sensitivity distribution of a photometric device, and the like are determined in advance, and through the calculation of a microcomputer photometric values are obtained which are equivalent to those obtained when photometry is conducted by a photometric device exhibiting a spectral sensitivity distribution equivalent to the spectral sensitivity distribution of a copying material, thereby to determine an exposure amount.
That is, if it is assumed that the spectral energy distribution of a light source used for photometry is P(.lambda.), the spectral sensitivity distribution of the photometric device is S(.lambda.), and development silver or a coloring dye on the film is .rho.(.lambda.), a density D photometrically measured by a photometric device having wavelength regions s to 1 is expressed by the following Formula (1): ##EQU1## where ##EQU2## is a bundle of rays made incident upon the film, and ##EQU3## is a bundle of rays transmitted through the film
Accordingly, the density D photometrically measured by the photometric device exhibiting a spectral sensitivity distribution equivalent to a spectral sensitivity distribution Sp(.lambda.) of the copying material, can be obtained if S(.lambda.) in Formula (1) above is substituted by the spectral sensitivity distribution Sp(.lambda.) of the copying material.
Since the spectral energy distribution P(.lambda.) of the light source and the spectral sensitivity distribution Sp(.lambda.) of the copying material are obtained by being measured in advance, if the spectral transmittance distribution .rho.(.lambda.) of the film, which differs depending on the type of film, is estimated, a density photometrically measured by the photometric device exhibiting a spectral sensitivity distribution equivalent to that of the spectral sensitivity distribution of the copying material can be obtained from Formula (1) above. Then, exposure amount can be determined on the basis of this density. In accordance with this method, since it is unnecessary to use a diffraction grating or a multiplicity of interference filters in the manner stated in the above-described prior art, the photometric device can be made compact and can be manufactured at low cost.
However, with the above-described method of calculation using the microcomputer, a method of accurately estimating the spectral transmittance distribution of the film has not been established, so that there has been a drawback in that photometric values obtained by the photometric device having a spectral sensitivity distribution equivalent to that of the copying material cannot be obtained accurately by calculation.
Furthermore, to determine the exposure amount accurately, it is preferable to determine the exposure amount after the image is divided into pixels by the sensors of the photometrically measuring section, and each pixel is separated into a multiplicity of colors and photometrically measured, and after the spectral distribution of the entire pixels is measured or estimated. However, there is a problem in that a long calculation period is required since the spectral distribution is calculated for each pixel. Furthermore, although it is necessary that the position of each pixel at the time when the image is divided by the sensors is accurately aligned at the actual position, to meet this requirement, it is necessary to effect the positioning of the sensors (so-called registration) with high accuracy. Therefore, much time is required in its adjustment.